Material Matters: Cork

Origins

As you could probably guess, cork comes from cork trees – cork oaks, or Quercus suber, to be specific. An evergreen – meaning that it retains its green leaves throughout the entire year – that’s believed to originate in the Mediterranean basin and date back to the Tertiary period (sometime between 66 million and 2.6 million years ago), cork oaks are endemic to southwestern Europe and northwestern Africa. Today, roughly 60 per cent of the world’s cork forests are in Portugal and Spain, while those two countries are responsible for 80 per cent of the world’s actual cork production.

Harvesting

Cork is harvested from trees between the months of May and August, when the bark can easily be separated from the tree itself without harming the underlying layer of phellogen beneath it. Before cork can be harvested, however, the tree needs to grow for about 25 years so that its trunk can reach a circumference of around 60 centimetres. Following the initial harvest, cork can subsequently be harvested again every nine to 13 years.

Best of all, though? Cork production is sustainable and environmentally-friendly, because it doesn’t require the actual tree itself to be cut down. Cork can also be recycled with ease, and transformed into new products.

Properties and Applications

So, why cork? Aside from its sustainable production, cork offers countless benefits that make it suitable for all kinds of uses.

For one, cork is naturally elastic and nearly impermeable; there’s a reason cork has been used as a bottle-stopper since the 17th century. Today, the byproducts of cork stopper production are transformed into brand new sheets that are then employed in everything from bulletin boards to tiling for walls and flooring. Since cork is naturally fire-retardant, it’s especially suitable for the latter, while its bubble-form structure of tiny air pockets makes it a natural insulator. Cork not only drastically reduces noise transmission, but can also save you money on your heating and cooling bills. Wool is the only natural product out there that’s better at keeping the heat in or out. Last but not least, cork’s low density means it’s perfect for buoys and fishing rods, as well as being a staple for the core of cricket balls, baseballs, and badminton shuttlecocks.

Applications in Footwear

Because of its elasticity, impermeablity, low density, and insulating properties, cork is especially well-suited for use in footwear – particularly when it comes to insoles. Because of this, cork has seemingly been a staple in footwear forever.

If you’ve ever seen a shoe dissection video, then you’ve probably noticed the layered construction that goes into making the sole of a dress shoe or boot – whether it features a Goodyear welt, Blake/McKay construction, moccasin construction, stitchdown construction, or a cemented sole, there are always layers of some kind. While layers of leather are natural and supremely durable, they can be stiff and make a shoe a bit heavyset. Synthetic foams, on the other hand, shed weight and provide more cushioning, but aren’t particularly durable. Cork, on the other hand, offers the best of both worlds, and is natural and durable while also being lightweight.

Better yet, cork will mould to the shape of a wearer’s foot over time, making it the perfect material for the insole of a shoe, and one that continues to be a go-to for modern dress shoes and boots alike. This is something a company like Birkenstock knows supremely well. By mixing cork with latex and other materials before baking it in a mould, the German-based sandal manufacturer is able to craft full cork footbeds.

Despite this, cork didn’t start hitting the realm of sneakers – at least amongst the heavy hitters – on the regular until relatively recently.

Sneakers

Cork had been used sporadically in sneakers by smaller and lesser-known brands for years before the giants got involved when Nike crafted 2012’s ‘King’s Cork’ release for LeBron James.

A nod to the post-game tradition of popping bottles after a big win, the ‘King’s Cork’ LeBron 10 celebrated James’s 2012 NBA Championship with the Miami Heat, putting a premium non-performance spin on his then-latest Swoosh signature. The ‘King’s Cork’ took the material’s use to new heights, though, by employing it in a completely non-traditional way. Instead of being relegated solely (sorry) to the insoles, cork was actually used for the the upper as well – coupled with leather lining, a matching tongue, and waxed cotton laces.

Full Circle

Interestingly enough, things have come full-circle with some of the Swoosh’s more recent releases: the React Element 87 brought cork back to the insoles with its 2018 debut as a more traditional juxtaposition to its contemporary and futuristic design elements. Now the upcoming Vapor Street PEG is going in the same direction, pairing cork insoles with Nike’s energy-returning React tooling, and a decidedly modern upper of mesh and seamless synthetic overlays.